1. Technical Field
The present invention relates to optical disks, such as a video disk, a compact disk, etc., that carries information that can be read by optical means.
2. Prior Art
An optical disk of the type shown in FIGS. 3(a) to 3(c) is conventional. Such an optical disk has a structure in which metal is deposited on a transparent substrate 1 by evaporation or sputtering so as to form a metal reflecting layer 2, and a protecting layer 3 is formed on the reflecting layer 2. Fine recess and protrusion portions (hereinafter referred to pits) corresponding to signals to be recorded are formed on the transparent substrate, and the reflecting layer 2 is made to have the same pit pattern. The transparent substrate 1 is made of a transparent resin material such as PMMA (polymethyl methacrylate), PC (polycarbonate), or the like, by a injection molding method, a compression molding method, a 2P method, or the like.
In a manufacturing process for the conventional disk, the material for the transparent substrate is injection molded using a stamper having the desired pit pattern. The desired pit pattern, arranged, spirally or concentrically is thus transferred to a main surface of the transparent substrate as shown at P in FIG. 3(a).
Next, as shown in FIG. 3(b), the metal reflecting layer 2 is formed on the surface of the transparent substrate 1 by an evaporation process. Finally, as shown in FIG. 3(c), the protecting layer 3, formed of a radiation setting resin capable of being hardened by radiation such as ultraviolet rays, is formed on the reflecting layer 2. Thus, the conventional optical disk is obtained.
Although a large quantity of conventional optical disks have been manufactured through an optical disk manufacturing process as described above, the conventional optical disks can not sufficiently satisfy the recent demand to form pits with higher density so as to make it possible to record larger quantities of information.